This invention relates to catheters. More particularly, the invention relates to dilitation catheters which have a shaft having a portion which can be inflated like a balloon. The balloon portion is expanded by supplying fluid under pressure after it is placed at a point in a blood vessel to increase the patency thereof.
The use of balloon catheters for enlarging the diameter of a blood vessel, for example, at a point of stenosis such as is produced by an accumulation of plaque, is a known medical practice. In one such procedure known as percutaneous transluminal coronary angioplasty, a flexible guide wire is first introduced percutaneously into an artery of a patient and is manipulated to arrive at and penetrate the lumen of the occluded portion of a coronary artery while the patient is viewed on an x-ray imaging screen. The guide wire is followed by a guide catheter which is fed along the guide wire to a point in the coronary artery which is just proximal of the occlusion. The dilatation catheter is then sent along the guide wire, within the guide catheter, into the patient's artery and the balloon portion of the catheter is positioned in the occluded portion of the artery.
One dilatation catheter used in this procedure consists of an inner tube, or cannula, which can pass freely along the guide wire. A catheter shaft surrounds the inner tube and has an inner diameter which is somewhat larger than the outer diameter of the inner tube. The distal end of the shaft comprises a flexible balloon portion which is sealed to the distal end of the inner tube and extends rearwards along the inner tube for short distance, where it is sealed to a more rigid shaft tubing. The balloon portion is capable of expansion when fluid under pressure is directed into the space between the shaft and the inner tube, while the rigid portion of the shaft is not.
After the balloon portion of the catheter is correctly positioned, as seen on the imaging screen, a fluid, such as a radiopaque contrast media under pressure, is introduced into the space between the inner tube and the shaft of the catheter so as to cause the balloon portion to expand and to press against the occluding matter on the inside of the blood vessel. The expansion of the balloon is carefully regulated to prevent possible over-expansion and over-stressing of the wall of the catheter which might cause it to rupture, while yet putting sufficient force on the blood vessel to accomplish the objectives of the procedure. When the desired enlargement of the occluded portion of the artery has been attained, pressure on the inside of the catheter is relieved, the balloon shrinks to its original size and is removed through the guide catheter. In some prior art catheters, lateral or axial shrinkage of the balloon which occurs at the time of deflation can result in undesirable curving of the distal end of the catheter.
In known catheter, for percutaneous transluminal angioplasty, the proximal end of the catheter comprises a mount which receives the proximal ends of the inner tube and of the shaft and seals them in spaced apart relationship, while providing a passageway for supplying fluid under pressure to the space therebetween. A spring within the mount exerts a force on the inner tube in the distal direction, relative to the mount. When the catheter is pressurized, the inner tube moves against the spring to accomodate the decrease in the length of the balloon which occurs when the balloon expands. Upon release of the pressure, the spring returns the inner tube to its distal position, and the diameter of the balloon is reduced to approximately its former diameter to ease removal of the catheter from the blood vessel. The possibility of curvature of the catheter and shift of position during inflation of the balloon are shortcomings of this device.
In catheters for coronary angioplasty a balloon of higher profile than the main shaft are currently in use.
Accordingly, there is a need for a catheter having a smooth profile and wherein the expanded balloon does not change position within the vessel site and which does not curl during inflation.